It is well-known in the art to prepare cationic oil-in-water emulsions of bitumen and to mix these emulsions with inorganic mineral aggregates. When mineral aggregates and the cationic emulsion are mixed, the emulsion will “break” due to the attraction between the positively charged bitumen droplets and the negatively charged aggregate surfaces. The cationic bitumen droplets will deposit on the aggregate surfaces and be bonded to the aggregates by the electrostatic action at the interface between the bitumen droplets and the aggregates. As emulsifiers, several salts between acids and amine compounds have been suggested. Frequently, acidified amidoamines, imidazolines, fatty polyamines, quaternary ammonium compounds, and mixtures thereof are used. The acid used normally is hydrochloric acid, but also phosphoric acids and other acids containing one or more acid hydrogen atoms have been used.
A variety of polyamines or derivates of polyamines have been used or suggested for use as emulsifiers or anti-stripping agents in bitumen compositions.
Thus, U.S. Pat. No. 3,259,512 discloses a branched polyamine where the branched group contains at least one nitrogen-bonded aminoalkylene group. These polyamines contain at least three primary amino groups and at least one tertiary amino group. The branched polyamines are used as de-emulsifiers for aqueous emulsions or as asphalt additives or as antistripping agents for asphalt-mineral aggregate compositions.
U.S. Pat. No. 3,518,101 describes an aqueous asphalt emulsion which contains, as an emulsifier, a salt between a polybasic acid selected from the group consisting of oxalic acid, tartaric acid, and citric acid, and a diamine compound containing an alkyl group having about 12 to about 22 carbon atoms. The amine groups could be primary, secondary and/or tertiary.
U.S. Pat. No. 3,615,797 discloses a method of making a bitumen with high adhesion properties by adding to the bitumen an ethylene oxide condensate of a long-chain alkyl triamine.
U.S. Pat. No. 4,967,008 discloses polypropylene polyamines which are partially methylated. The compounds are said to have surfactant properties and may, for example, be beneficial as asphalt emulsifiers and antistripping agents.
U.S. Pat. No. 5,073,297 discloses an aqueous bituminous emulsion-aggregate obtained by emulsifying bitumen in water with a particular cationic emulsifier which is a reaction product between modified polyamines and certain polycarboxylic acids and anhydrides. In the preparation of the bituminous emulsion, an acid solution of the emulsifier is used. For instance, hydrochloric, sulphuric, and phosphoric acid or the like can be added until a pH-value below 7 is reached and a clear emulsifier solution is obtained.
U.S. Pat. No. 6,048,905 describes a number of amine compounds suitable as an emulsifier for bitumen. For instance, the amine compounds can be monoamines or polyamines having an aliphatic substituent containing 8-22 carbon atoms. The amines can also be alkoxylated with ethylene oxide and propylene oxide.
When paving, it is today a general practice to prepare a cold mix in a plant and to transport the mix to the work site for paving. Therefore, it is of crucial importance that the mix retains a suitable consistency for paving for at least some hours after mixing. In addition, a strong cohesion between the bitumen and the aggregates as well as between the bitumen and the surface paved is essential. Further, a dense bitumen coating on the aggregates is desired.